GSM-noise "buzz" issue / ways forward

Andy Green andy at
Mon Sep 22 16:22:07 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| Is there any way to switch the audio path to some file output?
| i.e. can I (potentially) record "buzz" without an active GSM connection
| ( while irradiating the phone from an external HF source )
| would be cheaper and easier to set up that way.

Werner pointed out yesterday to a guy asking the same thing that


should be the thing.

As far as I know, nobody yet tested this with buzz and so confirmed that
the effective buzz problem actually comes at the MIC inputs to WM8753.

| <someone>
|>  Well maybe luckily we *might* eventually find a magic place for a
(33pF) C
|>  somewhere near Wolfson chip, to rework GTA02 out in the field this way.
|>  Anyway I'd rather expect this magic fix to be found by try and
error, rather
|>  than probing on a setup that's completely changed by mere applying a
probe to
|>  it.
| Could someone with the device open place 100Ohm resistor in series with
| 3/4pF from  the mic line to GND and test it? ( instead of the ferrite
| Is the trace in the top layer of the pcb or is it burried?

I don't have gerber layer data, but the bead was placed in series with
headphone jack p4, it should be possible to try.

But I don't have 3.. 4 pF caps lying around, I order some for tomorrow.

- -Andy
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